Three-phase brushless motor having auxiliary magnetic pole on rotor

ABSTRACT

The present invention relates to a three-phase brushless motor in which two electromagnetic transducer elements for detecting the rotation position of a rotor having a plurality of magnetized regions are disposed to have a relative positional relation with an electrical angle of 120° or 240°, a composed signal having a phase difference of 120° relative to the output signals from the electromagnetic transducer elements is provided and the drive current to be supplied to the stator coil is determined on the basis of the composed signal and the output signals from the electromagnetic transducer elements. An auxiliary magnetic pole having opposite polarity to that of main magnetic pole is disposed on the rotor at the portions near and opposing to the electromagnetic transducer elements so as to make the waveform of the composed signal of the output signals from the electromagnetic transducers steep at zero-cross points. Thus, the drive currents supplied to the stator coils are made excellent and uneven rotation torque can be improved.

DESCRIPTION Technical Field

So far flat and small three-phase brushless motor has been proposed asshown in FIG. 1. In FIG. 1, reference numeral 1 designates a stator, 2 arotor and 3 a rotary shaft. This stator 1 comprises six flat statorcoils L₁, L₂ . . . L₆ which are disposed on a base plate 4 of nearlycircular shape with an equal angular range, for example, an angularrange of 60° as shown in FIG. 2. In this case, a pair of opposing statorcoils L₁ and L₄ ; L₂ and L₅ ; and L₃ and L₆ are respectively connectedin series or in parallel to each other. The rotor 2 is formed of amagnet of disk shape in which eight poles of N poles and S poles arealternately magnetized with an equal angular range as, for example,shown in FIG. 3. Further, electromagnetic transducer elements, forexample, Hall elements H₁, H₂ and H₃ are respectively disposed on thebase plate of the stator 1 at its predetermined position, for example,at the intermediate position between the stator coils L₆ and L₁, at theintermediate position between the stator coils L₁ and L₂ and at theintermediate position between the stator coils L₂ and L₃ on the externalperipheral portion of the base plate of the stator 1. In this case,although the geometrical angle between adjacent Hall elements H₁, H₂ andH₃ is 60°, since the rotor 2 includes 8 poles, the Hall elements aredisposed with a relative positional relation of an electrical angle of240°.

As shown in FIG. 4, each of the Hall elements H₁, H₂ and H₃ is connectedbetween a voltage source terminal 5 and the ground. The output signalsfrom the Hall elements H₁, H₂ and H₃ are respectively supplied to acontrol signal generating circuit 6 which is formed of a semiconductorintegrated circuit. The six output terminals of the control signalgenerating circuit 6 are respectively connected to bases ofnpn-transistors 7a, 7b, 8a, 8b, 9a and 9b. The collectors of therespective transistors 7a, 8a and 9a are connected together to a voltagesource terminal 10 to which a positive D.C. voltage is supplied. Theemitters of the transistors 7a, 8a and 9a are respectively connected tothe collectors of the transistors 7b, 8b and 9b and the emitters ofthese transistors 7b, 8b and 9b are respectively grounded. Theconnection point between the emitter of the transistor 7 a and thecollector of the transistor 7b is connected through a series circuitformed of a series circuit of the stator coils L₁ and L₄ and a seriescircuit of the stator coils L₅ and L₂ to the connection point betweenthe emitter of the transistor 8a and the collector of the transistor 8b.While, the connection point between the stator coils L₄ and L₅ isconnected through a series circuit of the stator coils L₆ and L₃ to theconnection point between the emitter of the transistor 9a and thecollector of the transistor 9b. In this case, when the Hall elements H₁,H₂ and H₃ produce at their output terminals square wave signals havingphases each of which is sequentially different from one another by anelectrical angle of 240° as shown in FIGS. 5A, 5B and 5C, if a currentflowing through the series circuit of the stator coils L₁ and L₄ istaken as Ia, a current flowing through the series circuit of the statorcoils L₂ and L₅ as Ib and a current flowing through the series circuitof the stator coils L₃ and L₆ as Ic, the control signal generatingcircuit 6 is so formed that it generates control signals such that, asshown in FIGS. 5D, 5E and 5F, these currents Ia, Ib and Ic havedifferent phases by 120° each and each of them becomes a positivecurrent during 120° of the electrical angle, a zero current during thesucceeding 60° of the electrical angle, a negative current during thesucceeding 120° of the electrical angle and a zero current during thesucceeding 60° of the electrical angle, respectively, which is repeatedsequentially.

Since such prior art three-phase brushless motor requires the three Hallelements H₁, H₂ and H₃, there occurs such a problem that the number ofwires for interconnecting the Hall elements with a drive circuit islarge and the power for driving the Hall elements can not be neglectedin view of saving a power consumption. Further, when the motor isminiaturized, it is difficult to position the Hall elements with highprecision and the space for disposing the Hall elements is reduced.Thus, it is not desirable to provide three Hall elements as in the priorart.

Therefore, as shown in FIG. 6, a three-phase brushless motor ispreviously proposed in which two electromagnetic transducer elements,for example, two Hall elements H₁ and H₂ for detecting the rotationposition of the rotor 2 are respectively disposed with a relativepositional relation having an electrical angle of 120° or 240° and theoutput signals of the electromagnetic transducer elements H₁ and H₂ arecomposed with each other to thereby produce a composed signal having aphase difference of 120° relative to the output signals of theelectromagnetic transducer elements H₁ and H₂ so that on the basis ofthe composed signal and the output signals from the electromagnetictransducer elements H₁ and H₂, the drive currents are supplied to thestator coils L₁, L₂ . . . L₆. In the example shown in FIG. 6, the stator1 and the rotor 2 are formed similarly to those shown in FIGS. 2 and 3,in which of the Hall elements H₁, H₂ and H₃ as shown in FIG. 2, the Hallelement H₃ is removed, while the two Hall elements H₁ and H₂ areprovided. In this case, each of the Hall elements H₁ and H₂ is disposedto have a relative positional relation with an electrical angle of 240°.The D.C. voltage from the voltage source terminal 5 is supplied througha resistor 11 to the Hall elements H₁ and H₂ as the bias voltagethereof, and the output signals produced at one and the other outputterminals a₁ and a₂ of the Hall element H₁ are supplied to first andsecond input terminals of the control signal generating circuit 6, whilethe output signals produced at one and the other output terminals b₁ andb₂ of the Hall element H₂ are supplied to third and fourth inputterminals of the control signal generating circuit 6. Between the oneoutput terminal a₁ of the Hall element H₁ and the one output terminal b₁of the Hall element H₂ is connected a series circuit which is formed oftwo resistors 12 and 13, each resistor having an equal resistance valueR. The connection point between the resistors 12 and 13 is connected toa sixth input terminal of the control signal generating circuit 6. Onthe other hand, between the other output terminal a₂ of the Hall elementH₁ and the other output terminal b₂ of the Hall element H₂ is connecteda series circuit which is formed of two resistors 14 and 15, eachresistor having an equal resistance value R. The connection pointbetween the resistors 14 and 15 is connected to a fifth input terminalof the control signal generating circuit. In this case, the resistancevalue R of each of the resistors 12, 13, 14 and 15 is selected extremelylarger than those of the Hall elements H₁ and H₂. Further, in this case,if the values of the output voltage produced at one and the other outputterminals a₁ and a₂ of the Hall element H₁ are respectively taken as Vaand Va' and the values of the output voltages produced at one and theother output terminals b₁ and b₂ of the Hall element H₂ are respectivelytaken as Vb and Vb', a voltage value Vc applied to the fifth inputterminal of the control signal generating circuit 6 is expressed as

    Vc=1/2(Va'+Vb')

and a voltage value Vc' applied to the sixth input terminal of thecontrol signal generating circuit is expressed as

    Vc'=1/2(Va+Vb)

Thus, an input signal c between the fifth and sixth input terminals isgiven as

    c=Vc-Vc'=-1/2(Va-Va')-1/2(Vb-Vb')

An input signal between the first and second input terminals, namely, anoutput signal a of the Hall element H₁ is given as

    a=Va-Va'

and an input signal between the third and fourth input terminals,namely, an output signal b of the Hall element H₂ is given as

    b=Vb-Vb'

Thus,

    c=-1/2(a+b)

Accordingly, the detecting signals such as shown in FIGS. 5A, 5B and 5Care respectively supplied to the input terminals of the control signalgenerating circuit 6. In FIG. 6, the other circuit portions areconstructed similarly to those of FIG. 4 so that by the circuit shown inFIG. 6, the rotor 2 can be rotated similarly to that shown in FIG. 4.

According to the example shown in FIG. 6, the number of the Hallelements can be reduced from three to two, the number of the wires forinterconnecting the Hall elements with the drive circuit can be reducedand the power consumption can also be reduced, which facts areadvantageous for miniaturizing the motor.

However, when as the rotor 2 of the above three-phase brushless motor,such one in which the N poles and the S poles are alternately magnetizedwith the equal angular spacing as shown in FIG. 3 is used and this rotor2 is rotated, the waveforms of the output signals from the Hall elementsH₁ and H₂ become such ones having saturated flat tops as shown by curvesS₁ and S₂ in FIG. 7A. As a result, a waveform S₃ of the composed signalc, which is provided by composing the waveforms S₁ and S₂, has a verygentle inclination at zero-cross points as shown in FIG. 7A so that thezero-cross points can not be determined precisely. Thus a composedsignal c as shown in FIG. 7c being applied between the fifth and sixthinput terminals of the control signal generating circuit 6. The composedsignal c shown in FIG. 7C is such one that the phases of the fallingedges and the rising edges of the square wave are displaced from thenormal phases by τ₁, τ.sub. 2, τ₃ . . . . FIGS. 7B and 7D respectivelyshow waveforms which are obtained from the output signals S₁ and S₂ ofthe Hall elements H₁ and H₂. When the signals as shown in FIGS. 7B, 7Cand 7D are respectively supplied to the input terminals of the controlsignal generating circuit 6 so as to produce the drive currents whichare supplied to the stator coils L₁, L₂ . . . L₆ and the rotor 2 isrotated by such drive currents, the uneven rotation torque thereofbecomes large near the zero-cross points of the composed signal S₃ asshown in FIG. 7E. Then, there is a defect that a ripple becomes, forexample, 23.4% or above. In view of the above aspect, the presentinvention is to improve uneven rotation torque of a three-phasebrushless motor which uses two electromagnetic transducer elements.

DISCLOSURE OF INVENTION

The present invention is to provide a three-phase brushless motor inwhich two electromagnetic transducer elements for detecting the rotationposition of a rotor having a plurality of magnetized areas are disposedto have a relative positional relation with an electrical angle of 120°or 240°, a composed signal having a phase difference of 120° relative tothe output signals from the electromagnetic transducer elements isproduced, and the drive currents supplied to stator coils are determinedby the composed signal and the output signals from the electromagnetictransducer elements. In such a three-phase brushless motor, an auxiliarymagnetic pole having opposite polarity to that of the main magnetic poleis disposed on the rotor at a portion near and opposing to theelectromagnetic transducer elements so as to make the waveform of thecomposed signal of the output signals from the electromagnetictransducer elements steep at zero-cross points of the waveform of thecomposed signal. As a result, the drive currents supplied to the statorcoils are made satisfactory whereby to improve the uneven rotationtorque of the rotor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view showing an example of a three-phasebrushless motor of a flat type,

FIG. 2 is a plan view showing an example of a prior art stator,

FIG. 3 is a plan view showing an example of a prior art rotor,

FIGS. 4 and 6 are respectively diagrams showing examples of a drivecurrent supplying circuit,

FIGS. 5A-5F, 7A-7E, 9A-9E, 11A-11B are respectively diagrams useful forexplaining the present invention,

FIG. 8 is a plan view showing an example of a rotor used in anembodiment of a three-phase brushless motor according to the presentinvention,

FIGS. 10 and 12 are respectively plan views showing examples of rotorsused in other embodiments of the present invention, and

FIGS. 13A and 13B are diagrams showing an example of a rotor in a casewherein the present invention is applied to a cylindrical type motor.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a three-phase brushless motor according to the presentinvention will hereinafter be described with reference to FIG. 8. InFIG. 8, like parts corresponding to those in FIG. 3 are marked with thesame references and their detailed description will be omitted.

In this embodiment, the stator 1 is formed such that as shown in FIG. 2,six flat stator coils L₁, L₂ . . . L₆ are disposed on the base plate 4of substantially circular shape with an equal angular range, forexample, an angular range of 60°. In this case, the opposing statorcoils L₁ and L₄ ; L₂ and L₅ ; and L₃ and L₆ are respectively coupledserially or parallelly to each other. Further, the electromagnetictransducer elements, for example, Hall elements H₁ and H₂ arerespectively disposed at predetermined positions of the stator 1, forexample, at the intermediate position between the stator coils L₆ and L₁and at the intermediate position between the stator coils L₁ and L₂ inthe external peripheral portion of the stator 1. In this case, each ofthe Hall elements H₁ and H₂ are disposed to have a relative positionalrelation with an electrical angle of 240°. In this embodiment, theconnection relation among the Hall elements H₁, H₂ and the stator coilsL₁, L₂ . . . L₆ is made the same as that in FIG. 6.

In this embodiment, the rotor 2 is constructed as shown in FIG. 8. Thatis, the rotor 2 is formed such that, for example, eight poles of N polesand S poles are alternately magnetized on a disk made of magneticmaterial with an equal angular spacing as main magnetic poles 2a andauxiliary magnetic poles 2b having opposite polarities to those of themain magnetic poles 2a are magnetized on the disk at its externalperipheral portions defined by connecting adjacent intermediate pointsof the eight main magnetic poles 2a. In this case, the auxiliarymagnetic poles 2b of the rotor 2 are arranged to substantially pass overthe electromagnetic transducer elements H₁ and H₂ of the stator.

In this embodiment, similarly to the previously proposed three-phasebrushless motor using two Hall elements H₁ and H₂, the two Hall elementsH₁ and H₂ for detecting the rotation position of the rotor 2 aredisposed to have a relative positional relation with an electrical angleof 240°, the output signals from the Hall elements H₁ and H₂ arecomposed to each other so as to produce a composed signal which has aphase difference of 120° relative to the output signals from the Hallelements H₁ and H₂, and the composed signal and the output signals fromthe Hall elements H₁ and H₂ are used to determine the drive currentswhich will be fed to the stator coils L₁, L₂ . . . L₆. Thus, it ispossible to rotate the three-phase brushless motor.

In this case, according to this embodiment, when the rotor 2 is rotated,the waveforms of the output signals from the Hall elements H₁ and H₂ arenot saturated and become relatively steep waveforms as shown by curvesS₄ and S₅ in FIG. 9A because of the auxiliary magnetic poles 2b ofopposite polarities to those of the main magnetic poles 2a provided onthe portions of the rotor 2 near and opposing to the Hall elements H₁and H₂. A waveform S₆ of the composed signal c formed on the basis ofthe waveforms S₄ and S₅ becomes relatively steep at zero-cross points asshown in FIG. 9A and hence the zero-cross points are determined. As aresult, the composed signal c as shown in FIG. 9C is supplied betweenthe fifth and six input terminals of the control signal generatingcircuit 6. In the composed signal c as shown in FIG. 9C, the rising edgeand the falling edge of its square wave are determined by the zero-crosspoints of the waveform S₆. FIGS. 9B and 9D respectively show thewaveforms provided from the output signals S₄ and S₅ of the Hallelements H₁ and H₂. When the signals as shown in FIGS. 9B, 9C and 9D aresupplied to the input terminals of the control signal generating circuit6 which then produces the drive currents to be supplied to the statorcoils L₁, L₂ . . . L₆ and the rotor 2 is rotated by the above drivecurrents, its uneven rotation torque becomes relatively small as shownin FIG. 9E and a ripple can be reduced to, for example, 6.37%.

Further, FIG. 10 shows another embodiment of the rotor 2 according tothe present invention. In the embodiment of FIG. 10, two auxiliarymagnetic poles 2b of island shape having opposite polarities to those ofthe main magnetic poles 2a are symmetrically disposed near the externalperipheries of the main magnetic poles 2a. In this case, the auxiliarymagnetic poles 2b of island shape are respectively provided to haveelectrical angles of substantially 60°, 120°, 240° and 300° as shown inFIG. 10. When the stator for this rotor is constructed similarly asabove, the waveforms of the output signals from the Hall elements H₁ andH₂ become as shown by curves S₇ and S₈ in FIG. 11A. Since a waveform S₉of the composed signal provided by composing the curves S₇ and S₈becomes steep at zero-cross points of the composed signal, the waveformof the composed signal becomes steep at the zero-cross points as shownby the curve S₉ in FIG. 11A. Thus, the zero-cross points are determinedaccurately so that the excellent drive currents Ia, Ib and Ic can besupplied to the stator coils L₁, L₂ . . . L₆, thus the uneven rotationtorque being made extremely small as shown in FIG. 11B.

FIG. 12 shows a further embodiment of the present invention, and in theembodiment of FIG. 12, the auxiliary magnetic poles 2b of the rotor 2are respectively disposed at the inside of the main magnetic poles 2a.In this case, the Hall elements H₁ and H₂ of the stator are disposed soas to correspond to the auxiliary magnetic poles 2b, too. It is needlessto say that by the embodiment shown in FIG. 12, similar action andeffect as above can be achieved. Further, when the present invention isapplied to a motor of cylindrical type, the rotor thereof is constructedas shown in FIGS. 13A and 13B, in which the auxiliary magnetic poles 2bare disposed on the end surface of the rotor. According to theembodiment shown in FIG. 13, similar action and effect as above can beof course achieved.

Also it is needless to say that instead of the Hall element in the aboveembodiments, other electromagnetic transducer element such asmagnetoresistance element and so on can be used. Furthermore, while inthe above embodiments the two electromagnetic transducer elements aredisposed to have an electrical angular spacing of 240° therebetween, itwill be easily understood that they can be disposed to have anelectrical angular spacing of 120°. In addition, it is needless to saythat the present invention is not limited to the above embodiments butcan take various modifications without departing from the gist of thepresent invention.

We claim:
 1. A three-phase brushless motor in which two electromagnetictransducer elements to detect a rotation position of a rotor having aplurality of magnetized areas are disposed to have a relative positionalrelation with an electrical angle of 120° or 240° therebetween,respective output signals from said electromagnetic transducer elementsare composed to produce a composed signal having a phase difference of120° relative to said output signals from said electromagnetictransducer elements, and said composed signal and said output signalsfrom said electromagnetic transducer elements are used to determine adrive current which is supplied to a stator coil, characterized in thatan auxiliary magnetic pole having opposite polarity to that of a mainmagnetic pole is provided on said rotor at a portion near and opposingto said electromagnetic transducer elements whereby a waveform of saidcomposed signal of said output signals from said electromagnetictransducer elements is made steep at zero-cross points.
 2. A three-phasebrushless motor according to claim 1, characterized in that a magneticpole of each magnetized area of said rotor at a portion opposing to saidstator coil is an N(S) pole and a portion of said magnetized areaopposing to said electromagnetic transducer elements is formed of anN(S) pole of narrow width and auxiliary magnetic S(N) pole portionsdisposed at both sides of said narrow magnetic pole.
 3. A three-phasebrushless motor according to claim 2, characterized in that said statorcoil is formed of 6 coils and said rotor is formed of 8 magnetizedareas.
 4. A three-phase brushless motor according to claim 3,characterized in that said stator coils are formed of 3 pairs ofcircuits, each pair of which are serially coupled to each other and adrive circuit is provided to supply to each of said 3 pairs of circuitscurrents flowing in the different directions.
 5. A three-phase brushlessmotor according to claim 4, characterized in that said electromagnetictransducer elements are Hall elements, each of said Hall elements havingtwo output terminals and circuits, each formed of two resistors seriallycoupled to each other, are connected between output terminals ofdifferent Hall elements, whereby a composed signal is derived from aconnection point between said resistors serially coupled to each other.6. A three-phase brushless motor according to claim 5, characterized inthat an S(N) pole portion of island shape is provided on a part of theN(S) pole portion of each magnetized areas opposing to the stator coiland corresponding to electrical angles of substantially 60°, 120°, 240°and 300°.
 7. A three-phase brushless motor according to claim 6,characterized in that said S(N) pole portion of island shape is coupledto auxiliary magnetic pole at the portion opposing to saidelectromagnetic transducer elements.